Electrical control system



Oct. l5, 1946. P. T. Nnvls Erm. 2,409,581

ELECTRICAL CONTROL SYSTEI .y Filed Nov.` 30, 1944 5 Sheets-Sheet 1 l Je: I

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P. T. NIMS ETAL ELECTRICAL CONTROL SYSTEI Filed Nov. 30, 1944 5 Sheets-Sheet 2 /al I l. a... f v w s N. .f .r l I w z a a ma A L .H r j `f 02d #L M l F l/ 2 l. 3L 1 u 2 fl 2 u a u J o n 4 w u., 4; u 4 f 4 s l V IL Oct. l5, 1946.

Filed Nov. 30, 1944 P. T. NIMS ETAL l ELECTRICAL CONTROL SYSTEM 5 Sheets-Sheet 3 rf/44 MP* WIP www"

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ELECTRICAL CONTROL SYSTEM Filed Nov. 50, 1944 5 Sheets-Sheet 4 Oct. 15, 1946. P. T. MMS mL 2,409,581

M15@ MR ELECTRICAL CNTROL SYSTEM Filed Nov. 30, 1944 5 Sheets-Sheet 5 Patented Oct. 15, 1946 UNITED STATES PATENT oFFlcE ELECTRICAL CONTROL SYSTEM Paul T. Nims and Omer E. Bowlus, Detroit, Mich., assignors to Chrysler Corporation, Highland Park, Mich, a corporation of Delaware Application November 30, 1944, Serial No. 565,956

16 Claims. 1

The present invention relates to electrical control systems and is particularly directed to the provision of improved apparatus which functions as a combination converterdnverter for deriving alternating current energy of a desired adjustab-le frequency from a source of alternating current the frequency whereof may be randomly variable over a range which is above, below, or which includes, the output frequency. In its hereinillustrated embodiments the present invention is particularly designed for aircraft purposes, and serves to translate the variable frequency output of one or more engine driven generators into a three phase alternating current output of adjustably fixed frequency. In certain of its aspects the present invention is directed to improvement upon the inventions disclosed and claimed in the copending application of the present applicant, Nims, Serial No. 565,955, filed November 30 1944. Certain features disclosed but not claimed herein are claimed in the copending application of the present applicant, Bowlus, Serial No. 565,954, filed November 30, 1944.

Principal objects of the present invention are to provide a system of the aforesaid type which is simple in arrangement, requires a minimum number of structural elements, is relatively light in weight, and is reliable and eicient in operation; to provide such a system in which multiphase alternating current input energy is translated into multi-phase alternating current output energy; to provide such a system embodying improved means for timing the operations of the control apparatus associated with the several output phases; to provide such systems in which the multi-phase output circuits of the several units may be connected in parallel, and embodying improved means for synchronizing thecontrol apparatus of the several units; and to generally improve and simplify the construction and arrangement of systems of the above generally indicated type.

With the above as well as other and more detailed objects in view which appear in the following description and in the appended claims, a preferred but illustrative embodiment of the invention is shown in the accompanying drawings throughout the several views of which corresponding reference characters are used to designate corresponding parts and in which:

Figures 1A, 1B, 1C, and 1D collectively provide a diagrammatic arrangement of power and control circuits for two units of the present invention, arranged to supply a multi-phase output circuit in parallel with each other. In reading the drawings, Figure 1B may be placed immediately to the right of Figure 1A, Figure 1C may be placed immediately below Figure 1A, and Figure 1D may be piaced immediately below Figure 1B. When the drawings are so arranged unconnected terminals on the various sheets will line up with correspondingly designated unconnected terminals on the adjacent sheets, thereby completing the circuits which extend from one sheet to another; and

Figure 2 is a series of curves depicting various operating characteristics of the system.

It will be appreciated from a complete understanding of the present invention that in their broader aspects, the improvements thereof may be embodied in Widely differing systems, arranged for widely differing specific purposes. The system specifically disclosed herein is particularly designed for use on multi-engine aircraft, to furnish three phase alternating current for various control and operating purposes. The disclosure herein of the invention with particular reference to this application is, however, to be regarded in an illustrative and not in a limiting r Sense.

As is indicated above, it is desirable, in connection with modern aircraft, to provide selfcontained generating systems of the alternating current type, which are adapted to deliver alternating current at an adjustably xed frequency and voltage, and which utilize, as a prime source of power, alternating current generators which are driven by the aircraft engines. Since the aircraft engine speeds vary rather widely in operation, the frequency of the alternating current generatorsv also vary, making it desirable to provide apparatus which is effective to translate alternating current of a variable frequency into current having a frequency which is adjustably fixed, and which may fall below, within, or above the frequency range of the generator. The aforesaid copending application of the present applicant Nims, Serial No. 565,955, filed November 30, 1944, discloses and claims certain features of V such systems, which, as specifically disclosed, are

effective to deliver single phase alternating current. The present system on the other hand is arranged to deliver multi-phase alternating current, a three phase output being specifically i shown herein.

Figures lA and 1B show the power circuits for two substantially identical units, each comprising a main generator adapted to be driven for example by a corresponding engine of the asso ciatedaircraft and arrangements are shown for connecting the output circuits of the two units in parallel. Similarly, Figures lC and 1D show virtually identical control circuits for the power units of Figures 1A and 1B respectively and also show the synchronizing interconnections between such control systems. For these reasons a descn'ption of one power and one control unit will suilice for a description of both, except in the respects hereinafter noted.

Referring first to Fig. 1A, power is arranged to be delivered to the three phase output conductors Ill, I2, and I4, from an alternating current generator I6, through a combination converter inverter comprising three series of main electric valves 20-22-24-25-28-30; 32-34 38-43-42; and 44-45--48-5-52-54,

Generator I may be of usua1 construction and may be arranged to be driven either directly or, preferably, through suitable change-speed gearing, by a corresponding engine of the aircraft. Generator I6 is provided with a usual direct current iield winding E5 which, as described in the aforesaid Ninos application, may be provided with regulating apparatus which serves to .maintain the voltage of generator l5 at a substantially uniform value through the expected generator cperating speed range, which in the case of aircraft systems, may be from 4,000 to 10,000 R. P. M. Such regulating apparatus may also be arranged as described in the Nims application to maint a proper division of the load between two or more of the present power units when such units are operated in parallel with each other.

Each of the aforesaid main valves may he of any conventional type. Preferably and as indicated they are usually three element gas-filled grid controlled values of the so-called discontinuous type. That is to say, each of these valves, though normally non-conductive, may be rendered conductive, when their anodes are sufficiently positive with respect to their cathodes to sustain a discharge, by rendering their' grids suihciently positive with respect to their cathodes. When so rendered conductive, the grids lose control and the valves remain conductive until the anodes are either negative with respect to their cathodes or are not suiciently positive to sustain a discharge. It will be noticed that the cathodes of related groups of these valves are directly interconnected so that, although structurally separate rectiers are illustrated, multi-anode structures may be used instead. That is to say, for example, valves 20, 22, and 24 may be combined into a single multi-anode structure.

Generator I5 is illustrated as having six star connected phase windings A, B, C, D, E, and F, which are directly connected to the anodes of the corresponding main valves. That is to say, phase A is directly connected to the anodes of valve 2G, associated with output conductor I4, valve 42 associated with output conductor I2, and valve 48 associated with output conductor IG. Phase B in turn is connected to the anedes of valves 22, 38, and 4i', associated respectively with output phases I4, I2, and I0. Corresponding comments apply to the other generator phases, it being noted that each generator phase is associated with and is effective to supply current, under the conditions hereinafter stated, to one phase of the output circuit.

The cathodes of the main valves associated with output phase I4 are connected to the respective terminals of the primary winding 5!) of an associated transformer 62. Similarly, the cathodes of the main valves associated with output ph.se I2 are connected to the terminals of the primary winding Gil of an associated transformer and the cathodes of the main valves associated with output phase itl are connected to the terminals of the primary winding 68 of an associated transformer lo. Primary windings EQ, Ell, and 68 are provided with center taps which are connected through corresponding reactors l2, M, and I6 to the center tap "IB of the generator I. Reactors '12, M, and l5 may be and preferably are magnetically independent of each other, which relation is indicated by the dashed lines appearing therebetween.

Transformers 62, and lil provided with grounded secondary windings ai), and E34, which as shown, are directly connected to the corresponding load conductors Ifl, I2, and IU, which load conductors for the two parallel units are directly connected.

Commutating condensers Sii, 88, and 9d are connected directly across the corresponding transformers (it, and 'lil and serve to control the conductivity of the associated valves, in the hereinafter described manner.

To control the initiation and duration of the successive positive and negative half cycles of the output phases Isl, I2, and I3, and to determine the displacement, in electrical degrees, between the voltages induced in such phases, corresponding control transformers IGI), IM, and H34 are provided. These control transformers are provided respectively with center tapped primary windings Iili, itil, and IIB, and are also provided respectively with pairs of secondary windings I I2 and IIlI; IIE and IIB; and IZB and 22. The terminals of windings II2 and IIil are connected, respectively in series with current limiting resistors |24, between the grids and cathodes of valves 2U-22-2fl and ZSS--ZR-Sl Windings HB and IIB, and 12e and I2? in turn are correspondingly connected between the grids and cathodes of the remaining associated valves,

In accordance with this embodiment of the present invention, alternating voltages of approximately square wave form are induced in the secondary windings IIZ-IM--IIE IiE--l il-I22, the voltages in the two windings of each pair being 180 degrees out of phase with each other, and the voltages of the respective pairs being degrees out of phase with each other. The control circuits for eiecting such energization of the secondary windings of the control transformers are shown in Figures 1C and 1D, and are described hereinafter. As will be appreciated, and as is diagrammatically shown in portions IV, V, and VI of Figure 2, the above-described control Voltages render the grids of the associated main valves alternately positive negative with respect to their cathodes, so as to cause successive positive and negative half cycles of voltage to be induced in the respective output windings 33M 82-84.

It is believed that the operation ol the above described power circuits will be apparent from a description of the operation of the converter-inverter circuits associated with, for example, the output phase Ill. At the time t1 in Figure 2, control winding IIE becomes eiiective to positively bias the grids of valves 2--22-24, and winding i IQ becomes effective to negatively bias the grids of the associated valves EE--ZB-SII. As is described below, the latter action prevents any discharges in the lastmmentiened valves, and it will be understood. that the former action tends to render the valves 2 {1-22-24 conductive. At the time t1, phase A is most strongly positive and, because of the common cathode connections of the last-mentioned valves, this fact renders the cathodes of valves 22 and 24 positive with respect to their anodes and prevents the initiation of 'a discharge therethrough. Valve 20 is, however, conductivey and current may ow therethrough from phase A through the left-hand half of the associated primary transformer winding 60, and through the corresponding reactor 12. At the time tz in Figure 2, the potential of phase B rises to a value suiiiciently in excess of the voltage of phase A to render valve 22 conductive, and initiate a iiow of current from phase B through valve 22 and the left-hand half of primary winding E0. Conduction through valve 22 elevates the potential of the cathode of valve 20 to a value above that of its anode, and extinguishes the discharge through valve 20. Similarly, at approximately the time ts. the voltage of phase C rises to a Value above that of phase B, initiating a discharge through valve 24 and extinguishing the discharge through valve 22.

The aforesaid now of current from the source charges up the associated commutating condenser 86, bringing its left-hand terminal to a positive potential and its right-hand terminal to a negative potential. This full charge is preferably obtained just prior to each commutation point, in this case, t4. Throughout this interval, phases D, E, and F, are to varying degrees, positive, and the negative potential'established for their cathodes by winding Bl! and condenser 86, tends to cause flow of current through valves 26-28--30- Such current flow is prevented, however, by the strong negative bias applied to the grids of these valves by control winding I I4.

.t the time t4 in Figure 2, the polarities of windings I I 2 and I I4 are reversed, which reversed relation is maintained until the time te. The negative polarity of control winding I I2 negative ly biases valves 20-22--24 which action is without effect on valves 2D and 22 since these rectifiers are not conducting at the time t4. The negative bias applied to the conducting valve 24 tends to extinguish the discharge therethrough, and may, with certain classes of valves, be effective to do so.

The positive bias applied to valves 26-28-30 by control winding l I 4 tends to render all of these valves conductive. At the time t4, however, phase is more positive than phases D and E and consequently valve 26 is the only one of the justmentioned three valves which becomes conductive. This action initiates in the sense discussed below, the negative half cycle of voltage of output phase I4. As soon as valve 26 becomes conductive7 it elevates the right-hand terminal of condenser 85 to a value which is lower than the voltage of phase F by only the amount of the relatively small voltage drop through valve 26. By virtue of the charge then existing on condenser 86, this action immediately elevates the cathode potentials of all of Valves 20, 22, and 24 to values well above their anode potentials and extinguishes any discharges existing therein. The reversal of the charging voltage applied to condenser 86 when valve 2B becomes conductive enables the initial charge to dissipate itself through winding 60 and further enables a reverse charge to be built up on condenser 85. This reverse' polarity renders the cathodes of valves 20-22-24 strongly negative with respect to their anodes, which action is, however, ineiective to re-establish a discharge through any thereof in view of the negative bias applied to the grids. It

is to be noted that the time required for the discharge of condenser 8'6 is longer than the de-ionization. time of the just-mentioned valves. Consequently, the grids of these valves are enabled to obtain control thereof and maintain them non-conductive as aforesaid. It is believed to be evident that at the time t5, the now of current through winding 65 transfers from phase F and valve 26, to phase D and valve 28. Further, it is believed to be evident that at the time ts, at which time the original polarities of windings I I2 and l I4 are restored, valve 28 is extinguished, and the succeeding positive half cycle of output phase I4 is initiated from phase B through valve 22. It will be noticed from portion I of Figure 2 that with the assumed frequency relations between the input and the output circuits, that during the rst above described positive half cycle of the output phase I4, phases A, B, and C successively deliver current, through valves 20- Z2-24. During the iirst described negative half cycle on the other hand valves 26 and 28 carry the current, which is derived from phases F and D. During the positive half cycle represented by the interval reti, valves 22 and 24 conduct current from phases B and C. It will thus be apparent that the number of phases and valves which supply current to output phase I4 varies during successive half cycles of the same polarity and during successive half cycles of diierent polarity. The full lines in portion I of Figure 2 indicate the time intervals throughout which the correspondingly designated phases are effective to supply current to output phase I4.

Considering now the general form of the voltage wave induced in the secondary winding 8B of transformer 62, and the phase relation of this induced voltage relative to the output voltages of control transformer IM, it will be appreciated that so long as valves 253-22-24 are conductive they tend to cause a iicw of current through the left-hand half of the primary winding 60 of the associated output transformer, resulting in, for example, a positive-half cycle of induced voltage in secondary winding mi. Conversely, when valves 295--28--30 are conductive they tend to cause a flow of current through the right-hand half of winding Sil and induce a half cycle of voltage of negative polarity in winding Si). The impedances in the converter-inverter network delay the induced voltage in winding 8B by a, phase angle equal to a fraction of a half cycle of the output frequency. This delay or phase shift may, in a general sense, be explained as follows. At each commutation point, such as the time t4 in Figure 2. the commutating condenser 86 is charged, as aforesaid. When, at time t4, valve 26 becomes conductive, condenser 48 is enabled to elevate the potentials of the cathodes of valves 20-2 2-24 as aforesaid. Condenser 8S also elevates the potential of' the center tap of winding 60. These changes in potential are of course enabled by the associated reactor l2. The energy stored in condenser 86 prevents an immediate reversal of the induced voltage in winding 80, such induced voltage falling to zero only after the expiration ci an. interval determined in part at least by the characteristics of the previously described discharge circuit for condenser 85. Similar comments apply to the delayed reversal of the induced voltage in winding 8o which is initiated at each other commutation point such as the time te.

The form of the induced voltage wave in winding is .of course determined by the relative 'with output i. 1 described above with the exception that the control voltages applied to these banks are displaced ees with respect to each other and with to control voltages for cutout phase Portions II and III of Figure 2 ii full lines, the intervals, with respect to tde cor- "or voltages (portions V and VE ng which the indicated phases By examination of portions I, II, and III of Figure 2, it will be noticed that at any given time, Yr.- ei-rample, the time t1, phase is effective tc deliver current for each of output phases i4 and I2. Beginning at the time t2, in turn phase D ectV 'c to deliver current to each of output axes iE and iii. .A particular generator' phase, therefore, serves to deliver current to a plurallty of output phases at the same time.

So long therefore as the above-mentioned synchronously timed control voltages are developed by the control. transformers ll, ii-, an m4, the six phase variable frequency input po*` translated l o a three phase output having a :frequency equal to that of the energy applied to the control transformers. It will further be appreciated :from the :foregoing that the input and output frequencies are virtually independent of other, thus accommodating the system to the relatively unusual case in which the input nd output frequencies are identical, as well as to the more usual case in which they differ. It should he noted that the loading of the individual phases of the generator has a substantially uniform average value, for any given output load, although at certain frequencies, the average loading of the individual valves is not uniform. This circumstance nlakes it desirable, of course, to utilize valves of sufficiently large capacity to reliably handle any unbalanced loading conditions.

It will be appreciated that in the broader as pects of the invention, the main generator may be provided with a diderent number of phases than the illustrated six phases. For example, a three phase generator may be used, as disclosed in the aforesaid Nims application. In utilizing a three phase generator it will he appreciated that each phase winding is connected to twice the numb-er of anodes as in the present case. T'at is, a f )artieula-r phase vracing would be connected to all of the anodes to u sich, for examp phases A and D of the present generator are connected and so on.

Referring now to Figure illustrated gement for energizing the above described control transiorir'ers ifo, i'i., and Ulf! in the previously descrhed accurately t ned relation,

generally an oscillator' circuit i3d, whi .n Aserves as a source of periodic voltage; a counter-network |32, which serves to segregate successive impulses from the oscillator circuit 8 and appropriate them in proper order to the respective output phases; and a series of three inverter networks |34 which respond to the counter-network and control the delivery of energy to the respective control transformers Hill, |92, and |04.

The oscillator circuit |30 may, in general, be of any usual type and as illustrated, comprises a usual grid controlled gas-filled valve |40 of the previously mentioned discontinuous control type. Valve |46 is connected across terminals |42 and |44 of an illustrative source of power, in series with the primary winding of a synchronizing transformer |46, a timing condenser |48, and a potentiometer resistor |53. Usual gas-filled voltage regulating glow tubes |52 and |54 are interposed between terminals |42 and |44 and serve, as will'be understood, to maintain the voltage between these just-mentioned terminals at a substantially uniform value, terminal |44 being grounded and terminal |42 being indicated, for illustrative purposes, as having a potential of 240 volts. Neglecting the action of the synchronizing transformer h'l, it will be appreciated that when valve .1.40 is conductive, current is enabled to flow therethrough and charge up condenser |48, which current flow is surge-like in character. By virtue of the inductance in the plate circuit of the valve, the completion of this charging action is accompanied by a momentary reversal of the voltage across the valve which temporarily renders its cathode positive with respect to its anode. This action blocks the valve and enables the energy stored in condenser |48 to dissipate itself through resistor illu. As this charge is progressively dissipated, the potential of the cathode of valve |40 is correspondingly lowered, thereby progressively increasing the anode-cathode voltage across the valve. When the latter voltage reaches a critical value valve it again breaks down and passes an impulse of current. Valve |40 is thus rendered conductive and non-conductive periodically, at a frequency determined primarily by the characterof the discharge circuit for condenser |48, each conductive period being a very minor fraction of each non-conductive period. During each conductive period the potential of the adjustable tap |55 on resistor |50 abruptly rises and during each non-conductive interval, such potential gradually falls to a normal value. The potential of tap |55 is thus of the usual saw-tooth wave form, as indicated in portion VII of Fig. 2.

The corresponding oscillator for the companion unit (Figure 1D) duplicates the unit just described7 it being noted that `the secondary winding of each synchronizing transformer is tied to the grid of the oscillator valve |40 for the other unit. More particularly, the grid cathode circuit for valve |40 of the unit shown .in Figure 1C extends from the gro-und terminal |44 through the corresponding valve |49, conductor |58, thence through the secondary winding |5l of the companion synchronizing transformer |4 to the corresponding ground terminal |44 (Figure 1D). It will be appreciated accordingly that each time valve |4il of one unit breaks down, a voltage impulse is transmitted through the secondary winding of the corresponding winding synchronizing transformer- |46, which voltage impulse breaks down the Valve |40 associated With the other unit. The oscillator circuits for the two units are thus caused to operate in synchronisrn with each other.

It will be appreciated that the output frequency of each oscillator circuit is determined primarily by the desired output frequency of the power circuit and by the number of phases of the power circuit. In the present arrangement three output phases are provided and two impulses per output phase are required from the oscillator circuit. Accordingly, assuming a 400 cycle output frequency, it will be appreciated that the oscillator circuits are adjusted to have a frequency of 2,400 cycles per second.

Each counter-network comprises primarily a series of three valves, |62, |64, and |66, which preferably, lbut not necessarily, are of the high vacuum continuous control type. The cathodes of these valves are connected together and to the ground terminal |44. The anodes of these valves are connected, through control resistors |68, |10, and |12, to a supply conductor |14, which is maintained, by regulator valves |52 and |54, at an intermediate potential, of the order, for example, of 150 volts. The grids o-f Valves |62 and |64 are continuously tied to terminal |16, which is intermediate resistor |12 and the anode of valve |66, which grid circuits include resistors |18, |80, and |82. The grid circuit for valve |62 also includes a delaying condenser |84, which functions as hereinafter described. Similarly, the grid circuits of valves |62 and |66are tied to terminal |86, which is intermediate resistor and the anode of valve |64. These grid circuits include resistors |88, |90, and |92 and the just-mentioned grid circuit for valve |66 includes a delaying condenser |94. Finally, the grid circuits for valves |64 and |66 are tied to terminal |96, which is intermediate resistor |68 and the anode of valve |62. These grid circuits include as indicated a delaying condenser |98 and resistors 200, 202, and 204. The grids of all of the counter-tubes are tied, in parallel with each other, to the previously described oscillator terminal |56. Each such grid circuit includes a small blocking condenser 206. It will be appreciated accordingly that each time a positive impulse is applied to terminal |56, such impulse is transmitted to the grids of the three counter-valves and correspondingly elevates the potentials of these grids to a positive value with respect to their cathodes. The small blocking condensers 206 are charged up very quickly and consequently cause each such impulse to be of the sharply peaked form shown in portion VIII of Figure 2, the potential of terminal |56 being shown in portion VII of such figure.

The functioning of this counter-circuit, in general, is such that, at any given time, two of the three counter-valves are conductive and the remaining counter-valve is non-conductive. Each time a positive impulse is delivered from the oscillator circuit to the grids of 'these valves, the non-conductive valve is red or rendered oonductive. This action does not alter the conductivity of one of the remaining two valves but it does extinguish the remaining valve. Thus, for example, during an interval between two successive impulses of the oscillator circuit, valves |62 and |64 may be conductive and valve |166 may be non-conductive. The next impulse iires valve |66 and extinguishes valve |62, leaving valve |64 conductive. The next impulse from the oscillator circuit nres valve |62 and extinguishes valve |64, leaving valves |62 and |66 conductive. The next impulse from the oscillator circuit iires valve |64 and extinguishes valve 66. More particularly, operation of the counter-network is as follows: Assuming that valves |62 and |64 are conductive, it will be appreciated that terminals |96 and |36 have potentials which are above ground by only the amount of the voltage drops through ybetween ground and conductor |14 being consumed in resistors |68 and |10. The grids of valves |62, |64, and |66 are connected through resistors 208, 2|0, and 2|2, to terminal the potential whereof is somewhat below ground, for example, 35 to 50 volts below ground. The ratio of the resistors 204 and |90 (which are connected to the aforesaid terminals |96 and |86) to resistor 2|2 is such that under the conditions stated, the grid of valve |66 is negatively biased, which action renders valve |66 non-conductive. At the same time, the grids of valves |62 and |64 are connected through resistor on the one hand and resistor |82 on the other hand, to terminal |16. Since valve |66 is non-conductive, terminal |16 is at substantially the potential of conductor |14, which potential is very materially higher than that of terminals |96 and |86, and the last-mentioned connections thus serve to maintain the grids of valves |62-|64 at potentials which are slightly above ground and at which these valves are in wide-open condition.

It will be noticed that under the above described conditions the blocking condensers |84 and |98 receive charges, of the indicated polarities, the charge on condenser |84 attaining a value equal tothe drop across resistor |80 and the charge on condenser |98 attaining a value equal to the drop across resistor 202.

Assuming now.that the potential of terminal |56 associated with the oscillator circuit is abruptly elevated, as described above, by the now of a surge current through the oscillator valve |46, it will be appreciated that this action applies a peaked positive impulse, also as aforesaid, to the grids of each of the counter-valves |62, |64, and |66. This action of itself, is Without eifect on valves |62 and |64, in view of the fact that the grids thereof are already 'at wide-open positive values. This action does, however, positively bias the grid of valve |66 and renders this valve fully conductive. As soon as valve |66 becomes fully conductive, it immediately lowers the potential of terminal |16 to a value which is above ground only by the amount of the relatively small voltage drop through valve |66, which potential is substantially the same as the previously described potentials of terminals |96 and |86. The drop in potential of terminal |16 tends to but does not negatively bias the grid of valve |64, since this tendency is opposed by the impulse from oscillator circuit. The drop in potential of terminal |16, however, does immediately drive the grid of tube |62 to a negative potential, relative to its cathode, because of the charge on condenser |84. As soon as this action occurs, valve |62 becomes non-conductive and elevates the potential of terminal |96 to a value corresponding to the previously described potential of terminal |16,- that is to a potential substantially equal to that of conductor |14. With terminal |96 at the relatively high potential, the grids of valves |64 and |66 are held positive so that these valves are substantially wide-open, through circuits corresponding to those previously described in connection with valves |62 and |64. Similarly, with both valves |64 and |66 conductive, the. grid of valve |62 is negatively biased ina manner analogous to that previously described in connection with the negative bias on the grid of valve |66. The single described impulse from the oscillator circuit therefore serves to extinguish valve |62, leaving valves |64 and |66 conductive. It is believed to be evident that in an analogous manner, the next impulse 'from the oscillator circuit is effective, by firing valve |52, to extinguish valve |54, leaving valves |52 and |66 conductive. Similarly, a succeeding impulse is effective, by firing valve 564 to extinguish valve |66, leaving valves |62 and |54 conductive.

Each on or conductive interval of each countervalve is therefore equal in length to twice the period of the oscillator circuit, and each orf or non-conductive interval of each counter-valve is equal to one period of the oscillator circuit. Stated in another way each cycle comprising one on and one ofi interval of each counter-valve, is equal in length to three periods of the oscillator. Moreover, the cycles of the respective counter-valves have a phase displacement of one period of the oscillator; that is, a phase displacement of one third of a full cycle of each countervalve. These phase relations are indicated in portions IX, X, and XI, of Figure 2. Thus, assuming an oscillator frequency of 2,400 cycles, each counter-valve has a frequency of 800 cycles.

In the present system, each change from a nonconductive to a conductive condition of each counter-valve is utilized to trigger the corresponding inverter network |34. Each such inverter comprises a pair of high vacuum valves, designated 220, 222,224, 226, 228, and 236. Each such valve comprises main and auxiliary anodes, a control grid and an indirectly heated cathode. Usual screen grid valves are usable and are indicated in the drawings, the screen grids serving as the auxiliary anodes. Since these inver-ter networks are identical, a description of one thereof will sulce for all. Considering the inverter network associated with output phase I4, and which comprises valves 226 and 222, the cathodes of these valves are connected to the ground conductor 232. The anodes of these valves are connected to the corresponding terminals of the primary winding |66 of the associated control transformer |60, which winding has a center tap 236 which is continuously connected to supply conductor 238,

which is continuously maintained at a potential of, for example, 300 volts above ground. A stabilizing resistor 240 is connected across the primary winding |66. The screen grids 242 and 244 of valves 226 and 222 are continuously connected, through control resistors 246 and 248, to

a supply conductor 250 which is continuously maintained at a potential somewhat below the potential of conductor 238. For example, conductor 250 may be maintained at a potential of l approximately 240 volts above ground.

The control grid 252 of valve 220 is connected, through a network comprising a condenser 254 and a resistor 256, to terminal 253 which is intermediate resistor 248 and the anode of the companion valve 222. The control grid 266 of Valve 222 is similarly connected, through a network comprising resistor 262 and condenser 264, to terminal 266. Grids 252 and 26|) in turn are interconnected together through condensers 268 and 210. Conductor 212, which is connected to the anode of the corresponding counter-valve |62, is connected to terminal 214, intermediate the lastmentioned condensers. Conductor 212 includes a blocking condenser 216, and is connected to the ground conductor 232 through a relatively high resistance 218 and a continuously conductive rectifier 280, of usual form. Grids 252 and 266 are also connected, through associated resistors 282 and 284 to conductor 286 which is continuously 12 maintained at a potential well below ground; for example, at a potential of minus 240 volts.

At any given time one of the inverter valves 22B-222 is conductive and the companion inverter valve is biased to a non-conductive condition. A feature oi the present invention resides in utilizing the anode-cathode circuit of each inverter valve to supply the associated control transformer |66, through the above-mentioned connections; and in utilizing the screen grids of these inverter valves as auxiliary anodes to provide an output circuit for each valve to produce the inverter action. The inverter action may thus be described independently of the primary output circuits of these valves.

More particularly, and assuming that valve 220 is fully conductive, it will be appreciated that a substantial part, for example, two-thirds, of the voltage difference between conductor 256 and the grounded cathode is consumed in resistor 246, leaving terminal 266 at a potential which is above ground only by the amount of the voltage drop through valve 222.

The impedance of the network between terminal 266 and the negative conductor 286, and comprising resistor 262, condenser 264, and resistor 284 is such that terminal 288 of this network, to which grid 266 is connected, is at a sufliciently negative potential with respect to ground to completely bias valve 266 to a non-conductive condition. Under these conditions, the only voltage drop through resistor 248 is due to the current lowing in the network connection between conductors 256 and 286, and comprising resistor 248, condenser 254, resistor 256, and resistor 282. The impedance of this network is such that under the indicated conditions terminal 296, to which grid 252 is connected, is maintained at a potential with respect to the cathode of valve 22D, at which this valve is in a wide-open condition. Under the above conditions, further, condensers 268 and 21D contain variable charges, depending upon the stage of the inverter cycle then in progress.

`Each time counter-valve |62 changes from a conductive to a non-conductive condition, the potential of the associated terminal 292 abruptly rises, as will be clear from thel previous description. This increase in voltage, except in negligible part, is not communicated to terminal 214 of the inverter circuit, since under the indicated conditions, rectifier 260 affords virtually a shortcircut between conductor 212 and ground. Such increase in voltage does apply a potential to and charge up the small blocking condenser 216.

Each time counter-valve |62 becomes conductive, the potential of terminal 262 abruptly falls to a considerably lower value, as will be clear from the previous description. This action immediately pulls terminal 290 down to a potential which is below the potential of terminal 262 by the amount of the charge on condenser 216. The constants of the circuit, including terminals 29|) and 292, are such that the just-mentioned drop in the potential of terminal 296, produced by valve |62, is transitory in character.

The peaked negative impulse (portion XII, Figure 2) thus applied to terminal 296 serves to reduce the positive bias of the grid oi valve 220. This action in turn decreases current ilow between its cathode and its auxiliary anode or screen grid 242. The latter action in turn decreases the voltage drop across resistor 246, thereby elevating the potentials of terminals 266 and 1288 and opening up valve 222. The opening of valve 222 increases the drop across resistor 248 and correspondingly lowers the potentials of terminals 258 and 200. The lowering of the potential of terminal 290 still further reduces the conductivity of valve 220 which is reflected as an increase in the conductivity of valve 222. The above described negative impulse accordingly serves to initiate a progressive swing of valves 220 and 222, which swing takes place exceedingly rapidly, with respect to the frequencies involved in the present system, and serves to completely open valve 22.2 and completely block 01T valve 220.

The next time counter-Valve |62 becomes nonconductive, the positive impulse applied to terminal 292 is suppressed as before, making no change in the conductivities of the inverter valves. On the other hand, the next time counter-valve F62 becomes non-conductive, a peaked negative impulse is again applied to terminal 214. Since the inverter circuit is symmetrical, it will be appreciated that this negative impulse serves to block off valve 222 and render valve 220 fully conductive. Under the assumed conditions of a frequency cf 800 cycles for the action of countervalve 2, it will be appreciated that each f the inverter valves is thus cycled by the conductive and non-conductive conditions at the rate of 800 times a second, which corresponds to a frequency of the inverter circuit of 400 cycles.

Considering now the principal output circuits of the inverter valves, it will be appreciated that so long as inverter valve 220 is conductive, current flow in the corresponding portion of the primary winding of the associated control transformer |00 is in a direction to establish one polarity for the secondary or output windings ||2 and H4 of this transformer. So long as valve :222 is conductive, on the other hand, an opposite polarity is established for windings H2 and ||4.

As previously mentioned it is preferred that the output voltages of windings 2 and ||4 be of square wave form. Accordingly, in the present system, the impedance of the main anode-cathode circuits of inverter valves 220 and 222, are such that when either of these valves is rendered conductive, current through the corresponding main anode circuit rises gradually and substantially linearly to a maximum value, which is attained at approximately the same time that the nextJ inverter or flip-flop action occurs. When such action occurs current flow in the just-mentioned circuit is abruptly interrupted and a gradual rise in current flow through the main anode circuit of the other inverter valve is initiated. Current flow in the primary winding portions of the control transformer |00 is consequently of saw-tooth form and results in the approximately square wave form secondary outputs indicated in portion IV of Figure 2.

It is believed to be evident that the inverter networks comprising valves 224-22'@` and valves 228-230 function in the manner described above in connection with valves 220-222, in response respectively to the change from non-conductive to conductive condition of the associated countervalves |64 and |66. Consequently, transformers |0|l| 02| 04 deliver square wave secondary outputs having phase displacements of 120 electrical degrees, the frequency of such outputs being determined by the adjustably fixed frequency of the associated oscillator circuit |30.

A further feature of the present invention resides in providing means to properly synchronize the counter-networks for the several units.

' Referring to Figures 1C and 1Dtogether, it will be noticed that auxiliary valve 300` is provided.

This valve may be of usual three element high vacuum type. The anode of valve 300 is continuously connected to the grid 302 of valve |66 in Figure The cathode of valve 300 is continuously connected to terminal 214 Which as indicated is somewhat below ground, and the grid thereof is continuously connected to terminal 304, which is negative with respect to terminal 2 I 4. It will ce appreciated from a previous description that while valve |60 of Figure 1C is conductive, the potential of terminal 308 is relatively low. Assuming control switch 3536 is closed, with valve Se conductive, it Will be appreciated that the difference in potential between terminals 308 and Si@ is absorbed in condenser 3|2, leaving the grid of valve 300 negatively biased. The connection between valve 300 and valve |65 of Figure 1D is thus without effect. As soon, however, as valve of Figure 1C is extinguished, the potential of terminal 32S is abruptly elevated, thereby positively biasing valve 300 and rendering it conductive. When valve 300 is rendered conductive, it brings the potential of the grid 302 of valve |66 (Figure 1D) to a strongly negative value with respect to its cathode. If at the time this occurs, such valve `|6 is non-conductive (which is the condition assuming the counter-circuits for the two units are in proper step with each other) such negative biasing is without effect. If, however, the counter-circuits should be out of step with each other, such negative biasing would immediately extinguish valve |166 of Figure 1D. Such extinguishment would have the same effect as though it had been caused by an impulse by the associated oscillator circuit. The just-mentioned synchronizing circuit thus serves to insure, when the units are placed in operation, that they are in proper step with each other.

A further feature of the invention resides in the provision of improved means for insuring that the inverter networks for each unit are in proper step with each other, and to further insure that such inverter networks for a plurality of units are in step with each other. for such synchronization arises, as will be understood, from the fact that a negative impulse from, for example, counter-valve |62, is effective to fire one or the other of the two inverter valves 220 and 222, depending upon which of these valves was last fired. As shown, conductors 234 and 235 serve to :connect the control grids of valves 220 and 224 respectively, to the auxiliary anode or screen grid 231 of valve 230, through small blocking condensers 239 and 24|. It will be appreciated that in view of the phase relations `established by the counter-network, three of the inverter valves 2 20, and so forth, are conducting at any-given time and moreover each time inverter valve 220 is rendered conductive, valves 220 and 224 should already be in a conductive condition. It will be appreciated that each time inverter valve 228 is rendered conductive, the potential of screen grid 231 of valve 230 rises sharply. This positive impulse is communicated, through the blocking condensers 239 and 24| to the control grids of valves 220 and 224. If these valves are already conductive (which is the condition if the inverter circuits are in proper step with each other), these positive impulses are without effect. If, on the other hand, either of valves 220 and 224 should be non-conductive (which is the condition if the inverter networks are out of step) such positive impulse would immediately render the non-conductive valve conductive and bring the vcircuits The need into step with each other. It Wil be noticed that the above synchronizing circuits are provided for both units, Figures 1C and 1D.

In addition, in order to insure that the inverter networks for both units are in proper step with each other, the screen grid of valve 230 for the unit of Figure 1C, is arranged for connection, through a small blocking condenser 243 and a normally opened manually operable synchronizing switch 245, to the control grid 24'! of inverter valve 228 associated with the unit of Figure 1D. With this arrangement, it will be noted that each time inverter valve 228 of Figure 1C loecomes conductive, the consequent rise in potential lof the associated screen grid 231 of valve 230, causes a positive impulse to be transmitted to the control grid of valve 223 associated with the unit of Figure 1D. If this valve is already conductive (which is the condition if the inverter networks for the two units are in step) this positive impulse is without effect. On the other hand, if such networks are out of step, such impulse brings them into step.

In the present instance no source of energy for supplying the direct current power circuits have been indicated. It will ce understood that these power circuits may be supplied from any suitable source. For example, a. portion of the three phase output `of the system may he utilized for this purpose. Alternatively, and as is described in more detail in the aforesaid copending Nirns application, an auxiliary or pilot generator may `he provided to supply the control energy.

Although only a single complete embodiment of the invention has been described in detail, it will be appreciated that various modifications in the form, number, and arrangement of the parts may be made without departing from the spirit and scope of the invention.

What is claimed is:

l. In a system for delivering multiphase alternating current energy to an output circuit from a source of multiphase alternating current energy, a plurality of translating units each individual to a corresponding phase of said output circuit, each unit comprising a pair of electric valve each valve means dening a plurality of discharge paths having a common cathode connection and a plurality of anodes coupled to corresponding phases of said source, means coupling each pair of said valve means to the corresponding output phase so that current flow through the individual means of each pair tends to cause, respectively, current flow of respectively opposite polarity in the correspondn ng phase of the output circuit, periodically actuable control means for each unit so constructed and arranged as to provide for successively ren-- dering as an entity the corresponding valve means of each pair conductive and non-conductive in alternate relation so that current may flow from whichever anode ol the valve means is at the higher potential with respect to the common cathode potential of the valve means, and timing means for actuating the several control means in predetermined phase relation to each other.

2. The system of claim 1 wherein each phase of said source is common to all of said units.

3. The system of claim 1 wherein each phase of said source is common to one path of each valve means of each unit.

4. The system of claim l wherein each phase of said source is common to al1 or said units but is operatively connected to only one path in each Such unit.

5, Apparatus for supplying a multiphase load circuit comprising a plurality of systems each as defined in claim i. and means connecting the respective output circuits in parallel to said load circuit.

6. In a system for supplying a niultiphase load circuit comprising a plurality of systems each system having a plurality of translating units individual to said phases and common to said source, each unit including means actuable to translate energy from the source into single-phase alternating current energy and deliver the same to a corresponding phase of said output circuit, each system having control means for actuating the units of each system in predetermined phase relation to each other so that the respective phases of the output circuit of each system have corresponding phase relations, means connecting the respective output circuits in parallel to said load circuit, and means including regulating means for controlling the division, between said Luiits, of the energy supplied to said load circuit.

7. In a system for delivering multiphase alternating current energy to a load circuit from a source of multiphase alternating current energy comprising a plurality of systems each having an output circuit, each system having a plurality of translating units individual to a corresponding phase of its output circuit, each unit comprising a pair of electric valve means, each of said valve means defining a plurality of discharge paths having a common cathode connection and a plurality of anodes coup-led to corresponding phases of said source, means coupling the valve means in each unit to the corresponding output phase of its output circuit, so that current flow to the individual means of each pair tends to cause, respectively, current flow of respectively opposite plurality in the corresponding phase of the corresponding output circuit, periodically actuable control means for each unit of each system for successively rendering the corresponding valve means conductive and nonconductive in alternate relation, timing means for actuating the several control means oi each system in predetermined phase relation to each other, means connecting the respective output circuits in parallel to said load circuit, and means including regulating means for controlling the division, between said units, of the energy supplied to said load circuit.

8. In a system for supplying a multiphase alternating current output circuit from a source of electric energy, the combination of `a plurality of translating units individual to said phases and common to said source, each unit including means actuable to translate energy from the source to single-phase alternating current energy and delivering the same to a corresponding phase of said output circuit, a source of periodic control voltage common to said units, a counter-network including an electric valve individual to each phase of the aforesaid output circuit, control means coupling said valves to said source of periodic control voltage so that the conductivities of said valves are altered in predetermined succession, and means rendering each control means operably responsive to the condition of the associated said valve.

9. In a system for delivering multiphase alternating current energy to a load circuit from a source of alternating current energy having a plurality of phases, a plurality of translating units each individual to a corresponding phase of said load circuit, each unit comprising electric valve means defining a plurality of discharge paths the anodes whereof are connected to corresponding terminals of corresponding ones of said phases and additional electric Valve means deiining a plurality of discharge paths the anodes whereof are connected to corresponding ones of said phases, translating means for each unit connected between the cathodes of each of the valve means of the respective unit and another terminal of each of the phases which are connected to the anodes of the valve means of the respective unit and, current flow in each valve means tending to cause current flow in a corresponding direction in the corresponding translating means, control means for each of said units operable to alternately render the valve means conductive, and means coupling the load` circuit of each unit to the respective translating means so that successive current impulses passed by the respective valve means cause current flow in respectively opposite directions in the respective load circuits, and timing means for actuating each of said control means in predetermined phase relation to each other.

10. In a system for delivering multiphase alternating current energy to a load circuit from a source of multiphase alternating .current energy, a plurality of translating units each individual to a corresponding phase of said load circuit, each unit comprising .a pair of electric valve means, each Valve means defining a plurality of discharge paths having a common cathode connection and a plurality of anodes coupled to various phases of said source, an output circuit for each unit, each of said output circuits including a reactive device having opposite end connections and a center tap connection, means coupling the common cathode connections of one of each of said valve means of each unit to one end connection of the corresponding reactive device, means coupling the common cathode connection of the other of each of said valve means of each unit lto the other end connection of the corresponding reactive device, an impedance device for each pair of valve means, means coupling the center tap connection of each reactive device to the corresponding one of the impedance devices, means coupling said impedance devices to said source, and means for actuating said units in predetermined phase relation to each other so that the respective phases of the load circuit have correspondingl phase relations.

1l. In a system for delivering multiphase alternating current energy to a load circuit from a source of multiphase alternating current energy, a plurality of translating units each individual to a corresponding phase of said load circuit, each unit comprising a pair of electric valve means, each valve means dening a plurality of discharge paths having a common cathode connection and a plurality of anodes coupled to various phases of said source, an output circuit for each unit, each of said output circuits including a reactive device having opposite end connections and a center tap connection, means coupling the common cathode connections of one of each of said valve means of each unit to one end connection of the corresponding reactive device, means coupling the common cathode connection of the other of each of said valve means of each unit to the other end connection of the corresponding reactive device, an impedance device for each pair of valve means, means coupling the center tap connection of each reactive device to the corresponding one of the impedance devices,

means coupling said impedance devices to said source, a capacitor means connected between the common cathode connection of each unit, and means for actuating said units in predetermined phase relation to eachr other so that the respective phases of the load circuit have corresponding phase relations.

l2. In a system for delivering multiphase alternating current energy to an output circuit from a source of multiphase alternating current energy, a plurality of translating units each individual to a corresponding phase of said output circuit, each unit comprising a pair of electric valve means each dening a plurality of discharge paths having a common cathode connection and a plurality of anodes coupled to corresponding phases of said source, means coupling the valve means of each unit to the corresponding output phase so that current flow through the individual means of each pair tends to cause, respectively,

current iiow of respectively opposite polarity inl the corresponding phase of the output circuit, periodically actuable control means for each unit for successively rendering the corresponding valve means conductive and nonconductive in alternate relation, a source of periodic control voltage common to said units, a counter-network including an electric valve individual to each phase of the aforesaid output circuit, means coupling said valves to said source of periodic control voltage so that the conductivities of said valves are altered in predetermined succession and at a frequency of twice that of the output circuit, and means rendering each control means operably responsive to the condition of the associated said valve.

13. In a system for supplying a multiphase alternating current output circuit from a source of electric energy, the combination of a plurality of translating units individual to said phases and common to said source, each unit including means actuable to translate energy from the source to single-phase alternating current energy and delivering the same to a corresponding phase of said output circuit, a source of periodic control voltage common to said units, a counter-network including an electric valve individual to each phase of the aforesaid output circuit, means coupling said valves to said source of periodic control voltage so that the conductivities of said valves are altered in predetermined succession and at a frequency of twice that of the output circuit, and means including an inverter network individual to each phase of the output circuit, each such inverter network being operably responsive to the condition of the associated electric valve.

14. In a system for delivering multiphase alternating current energy to an output circuit from a source of multiphase alternating current energy, a plurality of translating units each individual to a corresponding phase of said output circuit, each unit comprising a pair of electric valve means each defining a plurality of discharge paths having a common cathode connection and a plurality of anodes coupled to corresponding phases of said source, means coupling the valve means of each unit to the corresponding output phase so that current flow through the individual means of each pair tends to cause, respectively, current iiow of respectively opposite polarity in the corresponding phase of the output circuit, periodically actuable control means for each unit for successively rendering the corresponding valve means conductive and nonconductive in alternate relation,` a source of periodic control voltage common to said units, a counter-network including an electric valve individual to each phase of the aforesaid output circuit, means coupling said valves to said source of periodic control voltage so that the conductivities of said valves are altered in predetermined succession, means including an inverter network individual to each phase of the output circuit, each such inverter network having a pair of valves, and circuit means operatively connecting said valves of said counter-network to said corresponding pairs of valves whereby alternate ones of each of said corresponding pair of valves are rendered conductive by consecutive alterations of the conductivity of said corresponding counternetwork valve.

15. In a system for controlling the phase angle and frequency of a multiphase alternating current circuit, the combination of a source of periodic control voltage common to all oi such phases, a counter-network including an electric valve individual to each such phase, means coupling said valves to said source of periodic voltage so as to render each of said valves conductive once each half-cycle of said circuit and conductive in rota tion, and means operably responsive to the conductivity of each valve for producing a control voltage for the corresponding phase.

16. In a system for controlling the frequency and phase angle of a multiphase alternating current load circuit electrically coupled to an input circuit, the combination of a source of pulsating control voltage common to such phases, means for controlling the frequency of the pulsating output of said voltage source at a frequency equal to two times the product of the desired frequency of the load circuit and the number of load-circuit phases, a counter-network including an electric` valve individual to each such phase, means coupling said valves to said source of periodic voltage so as to alter the conductive conditions of said valves in rotation, and means including an inverter network individual to each said valve and operably responsive to the condition thereof for producing control voltages for the corresponding phase.

PAUL T. NiMS. OMER E. BOWLUS.

Certificate of Correction Patent No. 2,409,581. October 15, 1946. PAUL T. NIMS ET AL.

It is hereby certed that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 3, line 37, for values read valves; column 5, line 43, for rectiers read valves; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the ease in the Patent Office.

Signed and sealed this 15th day of July, A. D. 1947.

LESLIE FRAZER,

First Assv'stcmt 'ommsszoner of Patents.

Certificate of Correction Patent No. 2,409,581. October 15, 1946. PAUL T. NIMS ET AL.

It is hereby certied that errors appear in the printed specication of the above numbered patent requiring correction as follows: Column 3, line 37, for values read valves; column 5, line 43, for rectiflers read valves; and that the said Letters Patent should be read With these corrections therein that the same may conform to the record of the ease in the Patent Oice.

Signed and sealed this 15th day of July,- A. D. 1947.

LESLIE FRAZER,

First Assvsta/nt Uommz'ssv'zmer of Patents. 

